Volcano distribution and tectonics: A planetoidic perspective

ABSTRACT Volcanic activity is ultimately controlled by processes that take place many kilometers beneath the surface of a planet. The deeper processes are unlikely to reach the surface without some degree of modification at shallower levels. Nevertheless, traces of those deeper processes may still be found when examining the final products at the surface. In this work, it is shown that it is possible to gain insights concerning the integrated contribution of deep structures through the study of the spatial distribution of volcanic vents at the surface. The method here described relies on the systematic use of increasing smoothing factors in Gaussian kernel estimations. The sequences of probability density functions thus generated are equivalent to images obtained with an increasing wavelength, which therefore have the power to penetrate deeper below the surface. Although the resolution of this method is much smaller than the resolution provided by seismic or other geophysical surveys, it has the advantages of ease of implementation, extremely low cost, and remote application. Thus, the reported method has great value as a first-order exploration tool to investigate the deep structure of a planet, and it can make important contributions to our understanding of the volcano-tectonic relationship, not only on Earth, but also across the various bodies of the solar system where volcanic activity has been documented.

Origin of shallow gas in the Dutch North Sea - Seismic versus geochemical evidence

In the Dutch offshore, we have observed numerous acoustic anomalies, usually bright spots, in seismic data of Cenozoic deltaic deposits. When associated with shallow gas, these bright spots are good indicators of resource potential, drilling hazard, or seabed methane emissions. We apply a combined seismic and petrophysical assessment to qualify the bright spots as direct hydrocarbon indicators (DHIs) for shallow gas and to exclude alternative sources of seismic anomalies. In some cases, we use other DHIs such as flat spots, velocity push-downs, transmission, and attenuation effects as estimators for gas saturation. A long-standing discussion concerns the sourcing and migration of shallow gas. Although vertical seismic noise trails (chimneys) tend to be seen as proof that shallow gas originates from the migration of deeper sourced thermogenic gas, the geochemical and isotope analyses almost exclusively indicate that the gas is of microbial origin and generated in situ in the Cenozoic strata. We conclude that the observed “chimneys” are most likely transmission effects, that is, artifacts that do not represent migration pathways of gas. Hence, we believe that for the Dutch offshore, the presence of shallow biogenic gas is not indicative of leakage of deeper thermogenic petroleum plays and cannot be used as an exploration tool for these deeper targets.

El rol de la exploración geofísica en acuíferos profundos en ambientes semiurbanos y rurales en cuencas de ante arco Andino, caso de estudio en acuífero del río Ñuble, Valle Central de Chile

The hydric resource coming from groundwater has a strategic nature at global scale, within a context of overpopulation and over exploitation of the resource and climate change. Chile doesn’t scape to it, where climate models predict a drought for most of the country, including partially, the agriculture region of the Central Valley between Santiago and Puerto Montt. The adaption process to global change demands the exploration new sources of provisions of this resource, being strategic the one coming from aquifers. To date, the knowledge of these resources is limited to depths below 200 m in each aquifer. However, in the Central Valley between Santiago and Chiloé, the geophysical evidences allow to infer the existence of a thick volcano-sedimentary basin growing in thickness southward well above 500m, with good potential for occurrence of large groundwater resources. The characterization of deep aquifers, 200-1,000 m of depth, demands to have an exploration tool economic, non-invasive, and reliable, able to be applied in semi-urban and rural environments, where the water resource need is higher. The geophysical methodologies meet these characteristics and have been applied in Chile and elsewhere as an exploration tool of ground water resources. However, its application have not been described in Andean environments, of large population and/or agro-industrial activity. In consequence, the present work raises a methodological strategy for the characterization of groundwater resources, in particular for the detection of deep resources. We propose the application of a combination of complementary geophysical techniques, including electrical, electromagnetic, and gravimetric methods (to determine the aquifer geometry) along with complementary techniques, like magnetometry, to reduce interpretation ambiguity and , constrained by hydrogeological information and petrophysics of rocks and sediments of the basin and basement. Complementary, we include an analysis of the potential effects of cultural noise and its effects on geophysical observations, given the focus of exploration in semi-urban and rural places. With the aim to validate the proposed methodology we use as a case study the aquifer of Ñuble river, in the Ñuble region, Chile. This aquifer properly represents an Andean forearc environment in rural and semi-urban condition, and potentially hosting a deep seated aquifer. The results allow the characterization of an aquifer with hydrogeological potential between 50 and 300-500 depth, overlying a sedimentary basin of more than 1,000 m thickness. The application of the proposed methodology for the exploration of groundwater resources will provide, in consequence, the recognition of a vital relevance resource for the sustainability of Chile during the following decades.

Spring Water Geochemistry: A Geothermal Exploration Tool in the Rhenohercynian Fold-and-Thrust Belt in Belgium

Spring water geochemistry is applied here to evaluate the geothermal potential in Rhenohercynian fold and thrust belt around the deepest borehole in Belgium (Havelange borehole: 5648 m MD). Fifty springs and (few) wells around Havelange borehole were chosen according to a multicriteria approach including the hydrothermal source of “Chaudfontaine” (T ≈ 36 °C) taken as a reference for the area. The waters sampled, except Chaudfontaine present an in-situ T range of 3.66–14.04 °C (mean 9.83 °C) and a TDS (dry residue) salinity range of 46–498 mg/L. The processing methods applied to the results are: hierarchical clustering, Piper and Stiff diagrams, TIS, heat map, boxplots, and geothermometry. Seven clusters are found and allow us to define three main water types. The first type, locally called “pouhon”, is rich in Fe and Mn. The second type contains an interesting concentration of the geothermal indicators: Li, Sr, Rb. Chaudfontaine and Moressée (≈5 km East from the borehole) belong to this group. This last locality is identified as a geothermal target for further investigations. The third group represents superficial waters with frequently high NO3 concentration. The application of conventional geothermometers in this context indicates very different reservoir temperatures. The field of applications of these geothermometers need to be review in these geological conditions.

Literature-Based Discovery beyond the ABC paradigm: a contrastive approach

Literature-Based Discovery (LBD) aims to help researchers to identify relations between concepts which are worthy of further investigation by text-mining the biomedical literature. The vast majority of the LBD research follows the ABC model: a relation (A,C) is a candidate for discovery if there is some intermediate concept B which is related to both A and C. The ABC model has been successful in applications where the search space is strongly constrained, but there is limited evidence about its usefulness when applied in a broader context. Through a case study of 8 recent discoveries related to neurodegenerative diseases (NDs), we show the limitations of the ABC model in an open-ended context. The study emphasizes the impact of the choice of source data and extraction method on the resulting knowledge base: different "views" of the biomedical literature offer different levels of accuracy and coverage. We propose a novel contrastive approach which leverages these differences between "views" in order to target relations between concepts of interest. We explore various parameters and demonstrate the relevance of our approach through quantitative evaluation on the 8 target discoveries. The source data used in this article are publicly available. The different parts of the software used to process the data are published under open-source license and provided with detailed instructions. A prototype of the system is also provided as an online exploration tool.

Monazite as an Exploration Tool for Iron Oxide-Copper-Gold Mineralisation in the Gawler Craton, South Australia

The chemistry of hydrothermal monazite from the Carrapateena and Prominent Hill iron oxide-copper-gold (IOCG) deposits in the IOCG-rich Gawler Craton, South Australia, is used here to define geochemical criteria for IOCG exploration in the Gawler Craton as follows: Monazite associated with IOCG mineralisation: La + Ce > 63 wt% (where La > 22.5 wt% and Ce > 37 wt%), Y and/or Th < 1 wt% and Nd < 12.5 wt%; Intermediate composition monazite (between background and ore-related compositions): 45 wt% < La + Ce < 63 wt%, Y and/or Th < 1 wt%. Intermediate monazite compositions preserving Nd > 12.5 wt% are considered indicative of Carrapateena-style mineralisation; Background compositions: La + Ce < 45 wt% or Y or Th > 1 wt%. Mineralisation-related monazite compositions are recognised within monazite hosted within cover sequence materials that directly overly IOCG mineralisation at Carrapateena. Similar observations have been made at Prominent Hill. Recognition of these signatures within cover sequence materials demonstrates that the geochemical signatures can survive processes of weathering, erosion, transport and redeposition into younger cover sequence materials that overlie older, mineralised basement rocks. The monazite geochemical signatures therefore have the potential to be dispersed within the cover sequence, effectively increasing the geochemical footprint of mineralisation.